Standard concentrated heparin: Patients in the concentrated heparin arm (enrolled in even calendar months) will receive a systemic loading dose of heparin of 15 units per kilogram of weight* by rapid (< 10 seconds) intravenous bolus. The heparin concentration for the rapid intravenous loading bolus for this arm is also 1000 units per mL. Then a maintenance rate of heparin of 7.5 U/Kg per hour will be started and delivered via a syringe on the Prismaflex® proximal to the dialysis filter. The concentration of heparin used will be 1,000 units of heparin per mL of 0.9% NaCl.